GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

6. MICROBIAL GROWTH

6.3. MICROBIAL NUTRITION

6.3.5. Transformation of Mixtures of Growth and Non-Growth Substrates by Microorganisms

In their natural habitats, microorganisms typically develop in the presence of multiple carbon substrates, whereas laboratory cultivation usually relies on monosubstrates as the sole source of carbon and energy. This significantly narrows our understanding of microorganisms. At the same time, numerous studies have demonstrated the ability of microorganisms to utilize mixtures of two or more Growth and non-growth substrates, and have investigated The regulation of such processes.

When a microorganism is capable of utilizing a mixture of growth substrates, two patterns of consumption are possible:

mixotrophy — the simultaneous, independent transformation of two (or more) growth substrates by microorganisms. Mixotrophy is characterized by the concurrent functioning of the assimilation Enzymes for both substrates. For instance, when the Yeast Hansenula polymorpha is grown on a mixture of growth substrates such as methanol and glucose, enzymes involved in the METABOLISM of both methanol and glucose are simultaneously present in the Cells;

diauxie — the sequential utilization of two growth substrates.

If both a growth substrate and a non-growth substrate are present in the culture medium, microorganisms may either ignore the presence of the non-growth substrate or transform it into specific products. Furthermore, if the transformation of the non-growth substrate occurs independently of the growth substrate, the process is referred to as non-growth oxidation.

If the transformation of the non-growth substrate is coupled with the assimilation of the growth substrate, the process is termed cometabolism. The most common scenario of cometabolism occurs when the non-growth substrate (also called a cosubstrate) is utilized as a source of energy.

Interestingly, under certain conditions, methane-oxidizing Bacteria are capable of growing on a mixture of substrates, none of which individually serves as a growth substrate for them. The ability of microorganisms to grow on a mixture of two or more non-growth substrates has been defined as syntabolism.